E-cadherin是一種重要的細胞黏著蛋白，它分布在adherens junction，參與許多重要的生理功能，像是生物發育、腫瘤生成、以及維持組織的結構等等。Echinoid (nectin的同系物)也是一種細胞黏著蛋白，與cadherin一樣的分布在adherens junction上，且會間接的與細胞骨架相連接。在我們實驗室之前的研究為了進一步探索echinoid的功能，我們設計了一種嵌合異構物：Ed-cad，它擁有echinoid的胞外區段以及cadherin的胞內區段。藉由在果蠅身上過度表現Ed-cad，我們想觀察這種異構物是否能取代內生性的cadherin或echinoid的功能。實驗意外的發現，過度表現Ed-cad會產生胞吞作用使得內生性cadherin表現量下降。於是，我們想要找尋產生這個胞吞作用的因子為何。目前已知胞吞cadherin的機轉，主要是透過clathrin的途徑。不過我們發現在過度表現Ed-cad的情況下，還有其它未知的途徑來參與胞吞作用。本文就是藉由果蠅基因組缺失的範圍掃描來找尋這個未知的因子。
在果蠅成蟲下過度表現Ed-cad會產生rough eye與翅膀缺陷的表現型。我們即利用這個特性，藉由掃描時觀察這些表型的變化來挑選可能參與影響的基因片段。實驗後發現，7個可能的候選片段被挑選出來，這些片段有些包含了已知參與細胞內運輸的蛋白基因，或是有潛力參與胞內運輸功能的基因，像是reck1、delta、sec10、Centaurin B1、lanB1、fuzzy onion等等。
這項研究目前還停留在一個很初步的階段。未來我們需要進一步針對這些可疑的基因進行單獨的測試，像是knockdown assay。我們也需要更多的生裡上的證據來證實這些基因的參與程度。

E-cadherin is the major cell adhesion molecule (CAM) of adherens junctions (AJs), and it involves in many important cellular physiology. Echinoid (Ed), a nectin homologue, also belongs to CAM and localizes to AJs. To take a deeper look on the function of Ed in our previous study, we generated a chimeric construct which has an extracellular domain of Ed with an intracellular domain of cadherin (Ed-cad), and overexpressed Ed-cad in Drosophila tissue to see if it could replace the function of Ed or cadherin. Surprisingly, overexpression of Ed-cad led to endogenous cadherin endocytosis, so we looked for the factors which participate in cadherin internalization in this situation. Cadherin can be retrieved by different mechanism, mainly via clathrin-mediated endocytosis in most situation. However, there were still other unknown factors which involved in cadherin internalization when overexpressing Ed-cad.
Overexpression of Ed-cad in adult Drosophila caused rough eye and wing defect. Here in this article, we used these features, and obtained Drosophila deficiency kit to generate a genome-wide screening to find out which factors may involve in cadherin internalization. After the screening, 7 genomic regions were identified, while some of them contain candidate genes which were already known or have the potential role involving in vesicular trafficking, including reck1, delta, sec10, Centaurin B1, lanB1, and fuzzy onion.
Nonetheless, the study presented here is only the initial work to find out the unknown factors of cadherin recycling. In the future, we have to examine the candidate genes one by one by such as knock down assay, and need more biological evidence to prove the exactly roles of these specific genes.

01. Halbleib JM, Nelson WJ. (2006). Cadherins in development: cell adhesion, sorting, and tissue morphogenesis. Genes Dev. 1;20(23):3199-214
02. Gumbiner BM. (2005). Regulation of cadherin-mediated adhesion in morphogenesis. Nat Rev Mol Cell Biol. 6(8):622-34
03. Takeichi M. (1995). Morphogenetic roles of classic cadherins. Curr Opin Cell Biol. 7(5):619-27
04. Cavey M, Rauzi M, Lenne PF, Lecuit T. (2008). A two-tiered mechanism for stabilization and immobilization of E-cadherin. Nature. 5;453 (7196):751-6
05. Lecuit T, Lenne PF, Munro E. (2011). Force generation, transmission, and integration during cell and tissue morphogenesis. Annu Rev Cell Dev Biol. 27:157-84
06. Holthöfer B, Windoffer R, Troyanovsky S, Leube RE. (2007). Structure and function of desmosomes. Int Rev Cytol. 264:65-163.
07. Harris TJ, Tepass U. (2010). Adherens junctions: from molecules to morphogenesis. Nat Rev Mol Cell Biol. 11(7):502-14
08. Takeichi M. (1991). Cadherin cell adhesion receptors as a morphogenetic regulator. Science. 22;251(5000):1451-5
09. Ireton RC, et al. (2002). A novel role for p120 catenin in E-cadherin function. J Cell Biol. 11;159(3):465-76
10. Chen YT, Stewart DB, Nelson WJ. (1999). Coupling assembly of the E-cadherin/beta-catenin complex to efficient endoplasmic reticulum exit and basal-lateral membrane targeting of E-cadherin in polarized MDCK cells. J Cell Biol. 22;144(4):687-99
11. Brigidi GS, Bamji SX. (2011). Cadherin-catenin adhesion complexes at the synapse. Curr Opin Neurobiol. 21(2):208-14.
12. Bryant DM, Stow JL. (2004). The ins and outs of E-cadherin trafficking. Trends Cell Biol. 14(8):427-34.
13. Delva E, Kowalczyk AP. (2009). Regulation of cadherin trafficking. Traffic. 10(3):259-67.
14. de Beco S, Gueudry C, Amblard F, Coscoy S. (2009). Endocytosis is required for E-cadherin redistribution at mature adherens junctions. Proc Natl Acad Sci USA. 28;106(17):7010-5.
15. Levayer R, Pelissier-Monier A, Lecuit T. (2011). Spatial regulation of Dia and Myosin-II by RhoGEF2 controls initiation of E-cadherin endocytosis during epithelial morphogenesis. Nat Cell Biol. 13(5):529-40.
16. Kaksonen M, Toret CP, Drubin DG. (2006). Harnessing actin dynamics for clathrin-mediated endocytosis. Nat Rev Mol Cell Biol. 7(6):404-14.
17. Pearse BM. (1976). Clathrin: a unique protein associated with intracellular transfer of membrane by coated vesicles. Proc Natl Acad Sci USA. 73(4):1255-9.
18. Akhtar N, Hotchin NA. (2001). RAC1 regulates adherens junctions through endocytosis of E-cadherin. Mol Biol Cell. 12(4):847-62
19. Lu Z, Ghosh S, Wang Z, Hunter T. (2003). Downregulation of caveolin-1 function by EGF leads to the loss of E-cadherin, increased transcriptional activity of beta-catenin, and enhanced tumor cell invasion. Cancer Cell. 4(6):499-515
20. Bryant DM, Kerr MC, Hammond LA, et al. (2007). EGF induces macropinocytosis and SNX1-modulated recycling of E-cadherin. J Cell Sci. 15;120:1818-28
21. Sharma M1, Henderson BR. (2007). IQ-domain GTPase-activating protein 1 regulates beta-catenin at membrane ruffles and its role in macropinocytosis of N-cadherin and adenomatous polyposis coli. J Biol Chem. 16;282(11):8545-56.
22. Mayor S, Pagano RE. (2007). Pathways of clathrin-independent endocytosis. Nat Rev Mol Cell Biol. 8:603-12.
23. Harris KP1, Tepass U. (2008). Cdc42 and Par proteins stabilize dynamic adherens junctions in the Drosophila neuroectoderm through regulation of apical endocytosis. J Cell Biol. 15;183(6):1129-43.
24. Palacios, F., et al. (2001). An essential role for ARF6-regulated membrane traffic in adherens junction turnover and epithelial cell migration. EMBO J. 20, 4973-86.
25. Glebov, O. O., Bright, N. A. and Nichols, B. J. (2006). Flotillin-1 defines a clathrin-independent endocytic pathway in mammalian cell. Nat Cell Biol 8:46-54.
26. Guha A, Sriram V, Krishnan KS. (2003). Shibire mutations reveal distinct dynamin-independent and -dependent endocytic pathways in primary cultures of Drosophila hemocytes. J. Cell Sci. 15; 116 :3373-86
27. Bulgakova NA, Klapholz B, Brown NH. (2012). Cell adhesion in Drosophila: versatility of cadherin and integrin complexes during development. Curr Opin Cell Biol. 24(5):702-12.
28. Wei SY, Modolell J, Hsu JC, et al. (2005). Echinoid is a component of adherens junctions that cooperates with DE-Cadherin to mediate cell adhesion. Dev Cell. 8(4):493-504.
29. Chang. L. H, et al. (2011) Differential adhesion and actomyosin cable collaborate to drive Echinoid-mediated cell sorting. Development 138(17): 3803-12
30. Ryder E, et al. (2007). The DrosDel deletion collection: a Drosophila genome wide chromosomal deficiency resource. Genetics. 177(1):615-29.
31. Freeman M. (1996). Reiterative use of the EGF receptor triggers differentiation of all cell types in the Drosophila eye. Cell. 15;87(4):651-60.
32. Brower DL. (1986). engrailed gene expression in Drosophila imaginal discs. EMBO J. 5(10):2649-56.
33. Ryder E, et al. (2004). The DrosDel collection: a set of P-element insertions for generating custom chromosomal aberrations in Drosophila melanogaster. Genetics. 167(2):797-813.
34. Cook RK, et al. (2012). The generation of chromosomal deletions to provide extensive coverage and subdivision of the Drosophila melanogaster genome. Genome Biol. 13(3):R21
35. Langevin J, et al. (2005). Drosophila exocyst components Sec5, Sec6, and Sec15 regulate DE-Cadherin trafficking from recycling endosomes to the plasma membrane. Dev Cell. 9(3):365-76.
36. Bernards A. (2003). GAPs galore! A survey of putative Ras superfamily GTPase activating proteins in man and Drosophila. Biochim Biophys Acta. 17;1603(2):47-82.
37. Jackson TR, et al. (2000). ACAPs are arf6 GTPase-activating proteins that function in the cell periphery. J Cell Biol. 30;151(3):627-38.
38. Kadrmas JL, Smith MA, Pronovost SM, Beckerle MC. (2007). Characterization of RACK1 function in Drosophila development. Dev Dyn. 236(8):2207-15
39. Bao S. (2014). Notch controls cell adhesion in the Drosophila eye. PLoS Genet. 10(1):e1004087.
40. Kusche-Gullberg M, et al. (1992). Laminin A chain: expression during Drosophila development and genomic sequence. EMBO J. 11:4519-27.
41. Urbano JM, et al. (2009). Drosophila laminins act as key regulators of basement membrane assembly and morphogenesis. Development 136(24):4165-76.
42. Koper A, Schenck A, Prokop A. (2012). Analysis of adhesion molecules and basement membrane contributions to synaptic adhesion at the Drosophila embryonic NMJ. PLoS One. 7(4):e36339.
43. Hales KG, Fuller MT. (1997). Developmentally regulated mitochondrial fusion mediated by a conserved, novel, predicted GTPase. Cell. 11;90(1):121-9.